stay Hydraulic system The following situations are often encountered: there is a large cavity at one end of the pipe, such as Hydraulic cylinder The accumulator is connected with the pipeline. A valve is installed at the other output end of the pipeline. Because the liquid volume of the chamber is large, it can be considered that the pressure in the chamber is constant. When the valve is opened, the liquid flow in the pipeline flows through the valve at a certain speed and is discharged. When the valve is suddenly closed, the liquid flow can no longer be discharged. At this moment, the liquid layer close to the valve is compressed, and the kinetic energy of this part of the liquid is converted into pressure energy. At this time, the liquid in other parts of the pipeline is still moving at a speed to the right under the inertial action, so the pressure in the pipeline starts from the valve and is pressed layer by layer to the left. If the length of the pipeline is L and the velocity of shock pressure wave propagation in the pipeline is C (that is, the velocity of sound in the liquid medium), the shock pressure will be transmitted to the large chamber within the time t1=L/C after the valve is suddenly closed. At this moment, all the oil in the pipeline stops flowing and is in a compressed state.

Since the pressure in the large volume cavity is lower than the transmitted impact pressure, the oil in the pipeline flows back to the large volume cavity, and the pressure of the liquid decreases layer by layer with the speed C to the right in turn. When t2=2L/C, it is transmitted to the valve. Since the valve is closed, the oil continues to flow back due to inertia, and the oil pressure at the valve further decreases, and the low pressure is transmitted to the left with the sound speed C, So continue to cycle. However, due to the energy loss of reciprocating flow, it will gradually decline to disappear. The hydraulic impact generated in the pipeline is called hydraulic impact in hydraulic hydraulics.

In the hydraulic system of machine tools, the inertia force of high-speed moving working parts can also cause pressure shock in the system. For example, when the working parts need to reverse or brake, a control valve is often used to close the oil circuit in the oil drainage pipeline. At this time, the oil can no longer be discharged from the hydraulic cylinder, but the moving parts still move forward due to inertia. After a period of time, the movement will stop completely. This will also cause the oil pressure in the hydraulic cylinder and pipeline to rise sharply, resulting in hydraulic shock.

Some elements in the hydraulic system are not responsive enough, which may also cause hydraulic shock. For example, when the pressure in the hydraulic system rises, the overflow valve cannot be opened quickly in time, resulting in pressure overshoot, or when the oil pressure rises, the oil delivery volume cannot be reduced in time, resulting in hydraulic shock.